Digital-to-analog (D/A) converters are used to process digital audio signals. Typically, digital data signals are received from a digital replay device or over a network, such as a cable television network. The signals are then processed by a D/A converter in an audio amplifier, cable receiver, or other audio device to produce an analog output within a frequency range that, when connected to a transducer such as a speaker, generates human audible sounds.
D/A converters used in high-fidelity audio processing typically include digital modulators that convert highly over-sampled digital values from high precision (e.g., 16-20 bits) to low precision (e.g., 1-3 bits), with the objective of substantially eliminating noise from the human audible band. However, quantization noise inherently increases with this reduction of precision.
To prepare these low precision signals for conversion to analog form, the signals are mapped into digital sequences. This process is known as sequence mapping. An analog signal is typically generated from the mapped digital signal. A sequence mapper can help to reduce additional noise which is caused by transition errors in the analog circuitry. The performance impact caused by these transition errors can be decreased by reducing the frequency of the modulator code transitions.
What is needed therefore is a sequence mapper that can be used in a D/A converter or A/D converter to improve performance by enabling a reduction of the frequency of modulator code transitions.
The present invention will now be described with reference to the accompanying drawings. In the drawings, like reference numbers can indicate identical or functionally similar elements. Additionally, the left-most digit(s) of a reference number may identify the drawing in which the reference number first appears.